FR2735222A1 - PROXIMITY HALL EFFECT SENSOR FOR DETECTING THE PRESENCE AND / OR PASSAGE OF A FERROMAGNETIC OBJECT - Google Patents

Abstract

The present invention relates to a Hall effect sensor, adapted to detect a ferromagnetic object (11), comprising an integrated circuit chip including a planar Hall element (14) which is positioned in, parallel to, and defines a sensor plane having a front side and a back side, and which element is perpendicular to, and centered on a sensor axis, and a magnetic structure (13) having an N pole and an S pole, the magnetic structure (13) being positioned behind the sensor plane and positioned so that an S pole and an N pole are adjacent to each other, and both are adjacent to the element.

Description

The present invention relates to a proximity sensor for detecting

  the presence and / or passage of an object

  ferromagnetic, such as a gear tooth.

  The present invention relates to a proximity sensor intended to detect the presence and / or the passage of a ferromagnetic object, such as a gear tooth, and more particularly such a "reaction" sensor comprising an assembly of a structure. magnetic and an integrated circuit chip having a Hall effect element, the chip being mounted at one end of the magnetic structure and

  in the magnetic field created by the magnetic structure.

  The Hall effect element generates an electrical signal relating to the resistance of the magnetic field perpendicular to the plane of the Hall effect element. When a ferromagnetic object approaches the Hall effect element, the resistance of the magnetic field perpendicular to the Hall effect element is changed. Thus the distance and physical orientation between the object and the Hall effect element are reflected in

  the electrical signal generated by the Hall effect element.

  This allows the Hall effect sensor to detect the distance

  between the sensor and the ferromagnetic object.

  A very suitable application for a sensor of this type is in the measurement of the rotational speed or the rotational position of a gear or a disc in the form of a gear. By placing this type of sensor near the periphery of the gear, the presence, proximity, passage and frequency of passage of the gear teeth

  in front of the sensor are reflected by the electrical signal.

  Thus, the sensor can be used as a tachometer, a tachometer, or to control a movement or a

rotational or linear position.

  The prior art Hall sensor uses a magnetic structure consisting of a permanent magnet

  cylindrical with a pole (N or S) at each flat end.

  The Hall chip is positioned near one end (and a pole), and the plane of the Hall effect element is parallel

  in the plane of the end of the magnet.

  The integrated circuit chips of these prior art proximity sensors almost always include an essentially linear Hall voltage amplifier to amplify the Hall output voltage. Many of these Hall integrated circuits also include a Schmitt trigger circuit to produce a binary output signal which goes from one level (a standby level) to the other binary level (an action level) when a ferrous object reaches a critical distance at which the magnetic field, perpendicular to a main face of the chip, exceeds a predetermined amplitude. These circuits are normally connected to DC, so that the sensor is capable of detecting ferrous objects passing at a zero frequency (for example one per year) up to a

  very high frequency (for example 100 kHz).

  This prior art sensor model was developed to detect the presence of a target, such as a tooth

  which was magnetized, that is to say, was it

  even a permanent magnet. Although in theory this model can work as a sensor for ferromagnetic objects, i.e. objects with high magnetic permeability, such as objects made of iron or iron alloys, the model does not work well in all applications. One reason for this deficiency, as will be discussed below, is the very baseline

  high or magnetic flux and no-object-present signal.

  In many application situations, the object-

  present is not much larger than the baseline signal, and the presence of electronic noise can

  make the prior art model unreliable.

  It turned out that a model with two Hall effect elements is an improvement in certain situations. By replacing the single Hall effect element with two closely spaced elements, electrically connected to neutralize each other in the baseline state, a good signal can be produced. Unfortunately, the signal is a baseline transition as each leading and trailing edge of a tooth passes in front of the sensor. In an appropriate situation, this is a useful sensor for measuring the frequency of passage of the teeth. However, this model does not provide a reliable indication of the presence or absence of a tooth or other

  object at power up.

  In many applications, the presence or absence of the tooth is used to communicate information to the sensor. For example, in a car engine, a gear could present a tooth to a sensor

  when a particular cylinder is in the ignition position.

  After initiating the engine ignition procedure, the sensor would retain fuel from the cylinder until the sensor detects the tooth. In this way, unused fuel would not be released into the atmosphere for

  startup, and pollution at startup would be reduced.

  Such a system could not use an unreliable signal or a signal which only detects the passage of an edge. These and other difficulties experienced with the devices of the prior art have been eliminated from a

  innovatively by the present invention.

  An object of the present invention is to provide a method for manufacturing a proximity sensor of Hall effect ferromagnetic objects, in which the sensor is highly sensitive to the presence or absence of objects.

  ferromagnetic in the sensor region.

  Another object of the present invention is to provide a proximity sensor of Hall effect ferromagnetic objects which is relatively insensitive in a proximity range and in a range of distance from the ferromagnetic object to the sensor. Another object of the present invention is to provide a gear tooth detector which generates an electrical signal which very clearly distinguishes between the present and the tooth-absent situation, at the time of energization, even for relatively gears. distant. Another object of the present invention is to provide a gear tooth detector which is designed so that the magnetic flux measured by a Hall effect element (i.e. a flux density perpendicular to the plane of l 'Hall effect element) is low in absolute value or equal to zero in the event of the absence or distance of the ferromagnetic object. According to the invention, a proximity sensor for ferromagnetic objects comprises a magnetic structure, an integrated circuit chip of the type including a Hall effect element and circuit means for generating a signal which is a function of the output of the element. Hall effect. The chip is installed relative to the magnetic structure, so that the chip is adjacent to at least two poles of the magnetic structure, and so that substantially all of the baseline magnetic flux passing through the Hall element is parallel in terms of the element to

Hall effect.

  The present invention relates to a Hall effect sensor, adapted to detect a ferromagnetic object, comprising an integrated circuit chip including a plane Hall effect element which is positioned on, parallel to, and defines a sensor plane having a front side and a rear side, and which element is perpendicular to, and centered on, a sensor axis, and a magnetic structure having an N pole and an S pole, the magnetic structure being positioned behind the plane of the sensor and positioned so that a pole S and an N pole are adjacent to each other and the

two are adjacent to the element.

  For the purpose of this description, a structure

  magnetic which has at least one N pole (or an equivalent pole piece) and at least one S pole (or an equivalent pole piece) with only one side of a magnet is called laminated magnet. If the laminated magnet is formed from layers of separate magnetized parts, then it is called a sandwich magnet. If it is formed from magnetized areas separately from a single piece of magnetizable material, then it is called a multipole magnet. If the magnetic structure provides a magnetic pole to the axis on the face of the magnet and the other magnetic pole on at least both sides of the axis (N-S-N or S-N-S), then it is

  called symmetrical laminated magnet.

  The Hall effect sensor is suitable for detecting the presence of a ferromagnetic object near the sensor, for detecting the distance between the sensor and a ferromagnetic object, for detecting the position of a ferromagnetic object relative to the sensor, and / or to detect the speed at which a ferromagnetic object passes in front

the sensor.

  A Hall effect sensor is provided in which the magnetic structure forms a magnetic detection field in front of the magnet and extending towards the front of the sensor plane, said field imposing a magnetic flux density component in and perpendicular to the Hall effect element, the value of the component being linked to the position

  of the ferromagnetic object in the field.

  A Hall effect sensor is provided in which the magnetic structure forms a magnetic detection field in front of the magnet and extending towards the front of the sensor plane, said field imposing a magnetic flux density component in and perpendicular to the Hall effect element, the value of the component being linked to the position of the ferromagnetic object in the field, and in which the value of the component has a baseline value which has an absolute value of almost zero Gauss and which occurs when the object is at a distance out of range of the sensor. The value close to zero has an absolute value less than or equal to 400 Gauss. The distance out of range is greater than or equal to 10 mm. The Hall effect element is 0.5 to 2.0 mm from the magnetic structure. Hall effect element is at a distance

  1 mm from the magnetic structure.

  A Hall effect sensor is provided in which the magnetic structure has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two parts, one of which has an N pole on the front face, and whose other

  has an S pole on the front face.

  A Hall effect sensor is provided in which the magnetic structure has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two parts, one of which has an N pole on the front face, and the other of which has an S pole on the front face, and one of these parts is moved back with respect to the face to adjust the magnetic baseline field created by the magnetic structure. A Hall effect sensor is provided in which the magnetic structure has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two permanent magnets, one of which has an N pole on the front face , and whose other

  has an S pole on the front face.

  A Hall effect sensor is provided in which the magnetic structure has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least one straight permanent magnet and at least one pole piece which is temporarily magnetized by its presence in the magnetic structure, one of which has an N pole on the front face, and of which

  the other has an S pole on the front face.

  A Hall effect sensor is provided in which the magnetic structure has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two permanent magnets and at least one pole piece which is positioned between the permanent magnets and which is temporarily magnetized by its presence in the magnetic structure, the permanent magnets having one of the magnetic poles on the front face, and the pole piece having the other pole

magnetic on the front.

  A Hall effect sensor is provided in which the magnetic structure has the shape of a cylinder with a magnetic axis and a flat front face adjacent to the chip and

parallel to the collector plane.

  A Hall effect sensor is provided in which the magnetic structure has the shape of a cylinder with a magnetic axis and a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two permanent magnets, of which one has an N pole on the front, and the other

  has an S pole on the front face.

  A Hall effect sensor is provided in which the magnetic structure has the shape of a cylinder with a magnetic axis and a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least one straight permanent magnet and at least one pole piece which is temporarily magnetized by its presence in the magnetic structure, one of which has an N pole on the front face, and the other of which has a pole

S on the front panel.

  A Hall effect sensor is provided in which the magnetic structure is in the form of a cylinder with a magnetic axis and a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two permanent magnets and at at least one pole piece which is positioned between the permanent magnets and which is temporarily magnetized by its presence in the magnetic structure, one of the permanent magnets having at least one of the magnetic poles on the front face, and the pole piece having the other pole

magnetic on the front.

  However, the principle of the invention can be best understood by referring to one of its structural forms, as shown in the accompanying drawings, in which: FIG. 1 is a schematic view in which the general characteristics of sensor systems relating to the present invention; Figure 2 is a schematic view showing the manner in which the present invention replaces the magnetic structure behind the chip in Figure 1 with a laminated magnetic structure which has both the S pole and the N pole at the back of the chip and adjacent to each other; FIG. 3 is a plan view along the axis of the magnet which is perpendicular to the face of the laminated magnet, to the front and rear faces of the chip and to the plane of the Hall effect element in the chip; Figure 4 is a view of the preferred model of the magnetic structure, with a view of the main face of the magnet; Figure 5 is a side view of the preferred model of the magnetic structure; FIG. 6 is a perspective view of the preferred model of the magnetic structure, the axis extending upwards and out of the paper from the main laminated face; FIG. 7a is a flow diagram showing the variation of magnetic field as a function of the air gap between the Hall effect element and the gear in a construction previously designed with a single pole of the magnet adjacent to the element to Hall effect and configured to control the passage of ferromagnetic gears; Figure 7b is similar to Figure 7a except that Figure 7b uses a target with wider teeth and a wider space between the teeth; FIG. 8 relates to the laminated configuration of the present invention and is a flow diagram on energizing the flux density in Gauss, for various air gaps (distances between teeth and sensor) relative to the rotation of the target (gear ); Figure 9 is similar to Figure 8 in that both relate to the laminated configuration of the present invention; FIG. 10 presents a diagram of density of flux through the face of a sandwich magnet (NSN) in which two magnets with N poles opposite are separated by a pole piece which is aligned on the face and has a pole S to the face; Figure 11 shows the effect of the position of the magnet relative to the rear of the Hall effect element on the intensity of the base field, for a magnet sandwiched with an aligned T-shaped pole piece ; Figure 12 shows the effect of moving the pole piece back from the face of the magnet by Z mm on the baseline flux density (presence of pits) through the face of a piece sandwich magnet polar T; FIG. 13 shows a flow diagram through the face of a sandwich magnet with a T-shaped pole piece with a pole piece moved back by 1.5 mm; figure 14 is similar to figure 13 except that the magnet used to generate the data of figure 14 is a sandwich magnet in which the central element is an inverted straight magnet (it is not a T and not only a pole piece) also shifted backwards by 1.5 mm; FIG. 15 shows a Hall effect single-pole gear tooth sensor 10 of the type known in the prior art; Figure 16 shows a schematic representation of a gear which is moved to a position quite distant from the sensor shown in Figure 15, and the gear teeth being positioned on either side of the sensor so that the sensor detects the space between teeth; Figure 17 shows the sensor and the gear of Figure 16 o the gear is rotated to bring the tooth to its closest position on the rotation path; Figure 18 shows a gear which is positioned even closer to the sensor than that of Figure 16; Figure 19 shows the rotation of the gear shown in Figure 18 so that the gear tooth is in its position closest to the sensor; Figure 20 shows a schematic view of the present invention, as it corresponds to the structure of the prior art shown in Figure 15. In Figure 20, the magnetic face on which the Hall effect sensor is mounted is shown as a laminated structure; FIG. 21 shows the effect of moving the gear to be detected towards a position relatively distant from the sensor; Figure 22 shows the effect when the gear shown in Figure 21 is rotated to bring the tooth close to the sensor; Figure 23 shows an arrangement in which the gear, although still in position between two teeth, is placed even closer to the sensor than the arrangements shown in Figures 21 and 22; FIG. 24 shows a position in which the rotation of the gear positioned in FIG. 23 moves the tooth closest to the sensor; Figure 25 is a graphical representation of the Hall effect flux density detected in the various configurations shown in Figures 15 to 24; Figure 26 is a perspective view of a magnetic structure which includes four magnetized poles and one face; Figure 27 is a perspective view of a magnetic structure which includes two poles, one face, and a steel tray; Figure 28 is a perspective view of a magnetic structure which includes four poles, one side with a steel plate; Figure 29 is a perspective view of a magnetic structure which includes a pole parallel to the thickness, with a steel plate and a central pole; Figure 30 is a perspective view of a magnetic structure which includes a pole parallel to the thickness with a steel cup; Figure 31 is a perspective view of a magnetic structure which includes a pole parallel to the thickness, with a steel cup and a central pole; Figure 32 is a perspective view of a magnetic structure which includes three alternating magnets with a steel tray; Figure 33 is a perspective view of a magnetic structure which includes a pole parallel to the thickness with a steel angle; Figure 34 is a perspective view of a magnetic structure which includes a pole parallel to the thickness with a steel channel; Figure 35 is a perspective view of a magnetic structure which includes poles parallel to the thickness, with two lateral steel plates; Figure 36 is a perspective view of a magnetic structure which includes two magnetized poles and a face (through); Figure 37 is a perspective view of a magnetic structure which includes three magnetized poles and one face (through); Figure 38 is a perspective view of a magnetic structure which includes two magnetized poles and one face (through), with a steel plate; Figure 39 is a perspective view of a magnetic structure which includes two magnets with a steel tray; Figure 40 is a perspective view of a magnetic structure which includes three magnetized poles and one face (through), with a steel plate; Figure 41 is a series of perspective views of magnetic structures which have multiple poles on one side; Figure 42 is a sectional view of an application environment in which the sensor assembly of the present invention can be used, and more specifically, the figure shows the end of a wheel axle of a car ; Figure 43 is a computer model of the effect of a rectangular ferromagnetic target 11a on the magnetic field around a magnetic structure 15a showing the principles of the present invention; FIG. 44 corresponds to FIG. 43 and shows how the displacement of the target 11a towards the magnetic structure causes the lines of flux between the target and the magnetic structure to concentrate axially inwards; Figure 45 shows the flux density across the face of a magnetic structure which has only one N pole and one S pole on the back of the sensor chip; Figure 46 shows the gear passing signal produced by the magnetic structure shown in the figure; FIG. 47 is a table comparing the characteristics of a Hall effect element and a

  substitute called magnetoresistant element.

  Referring first to Figure 1, which shows the general features of sensor systems 100 relating to the present invention, the system includes a ferromagnetic target 11, such as a steel gear, an effect sensor chip Hall 12, and a magnetic structure 13. In FIG. 1, the magnetic structure is of the conventional type of straight magnet, the pole S being at one end adjacent to the chip, and the pole N at the other end. This system can have one or two Hall 14 elements in the chip, both choices,

  as described above, pose problems.

  As shown in FIG. 2, the present invention replaces the magnetic structure 13 behind the chip with a laminated magnetic structure 15 which has both the S pole and the N pole on the rear face of the chip and adjacent one to the other. 'other. This arrangement creates a more suitable magnetic field around the Hall effect planar element 14. Figure 2 shows a simple sandwich construction in which two straight clad magnets 16 and 17 are fixed on a central bar 18. The central bar 18 could be a permanent magnet oriented with its poles opposite those of the plating magnets. Alternatively, the central bar could be a pole piece which has a high magnetic permeability (easily conducts the flow

  magnetic), but is not itself a permanent magnet.

  The plating magnets would induce temporary magnetism in the pole piece and cause it to react like an opposite pole magnet, as long as the sandwich structure is maintained. In both cases, the magnetic structure has both the S and N poles at the back of the chip and exposes the Hall effect element to the magnetic field that exists in front of the multipolar surface. Such a construction can also be achieved by using a single piece of permanently magnetizable material which has been magnetized into three separate areas to form the polar structure described above. Figure 3 is a plan view along the axis of the magnet. The axis is perpendicular to the face of the laminated magnet, to the front and rear faces of the chip and to the plane of the effect element

Hall in the chip.

  Figures 4, 5, and 6 show the preferred model of the magnetic structure. Figure 6 is a perspective view of the preferred model of the magnetic structure, the axis extending upward and out of the paper from the main laminate face. A longitudinal plate is shown and allows electronic conductors, from a chip mounted on the main face, to pass along the length of the magnet without extending outside the circular pattern profile of the cross section of the magnet parallel to the main magnet face. Figure 4 is a view of the preferred model, with a view of the main magnet face. Figure 5 is a side view of the preferred model. The magnetic structure can take many forms, as will be described below. The essential characteristic is that the magnetic structure must form a magnetic field around the Hall effect element, which field produces the effects when the element is adjacent to

  two different poles that are adjacent to each other.

  Typically the two poles are presented on the rear face of the CI Hall. The decline of one or more poles can

optimize the field.

  The present invention relates to a Hall effect sensor, adapted to detect a ferromagnetic object, comprising an integrated circuit chip including a planar Hall element which is positioned in, parallel to, and defines a sensor plane having a front side and a rear side, and which element is perpendicular to, and centered on, a sensor axis, and a magnetic structure having an N pole and an S pole, the magnetic structure being positioned behind the sensor plane and positioned so that a pole S and an N pole are adjacent to each other and the

two are adjacent to the element.

  The Hall effect sensor is suitable for detecting the presence of a ferromagnetic object near the sensor, for detecting the distance between the sensor and a ferromagnetic object, for detecting the position of a ferromagnetic object relative to the sensor, and / or to detect the speed at which a ferromagnetic object passes in front

the sensor.

  A Hall effect sensor is provided in which the magnetic structure forms a magnetic detection field in front of the magnet and extending towards the front of the sensor plane, said field imposing a magnetic flux density component in and perpendicular to the Hall effect element, the value of the component being linked to the position

  of the ferromagnetic object in the field.

  A Hall effect sensor is provided in which the magnetic structure forms a magnetic detection field in front of the magnet and extending towards the front of the sensor plane, said field imposing a magnetic flux density component in and perpendicular to the Hall effect element, the value of the component being related to the position of the ferromagnetic object in the field, and in which the value of the component has a baseline value which has an absolute value of almost zero Gauss and which occurs when the object is at a distance out of range of the sensor. The value close to zero has an absolute value less than or equal to 400 Gauss. The distance out of range is greater than or equal to 10 mm. The Hall effect element is 0.5 to 2.0 mm from the magnetic structure. Hall effect element is at a distance

  1 mm from the magnetic structure.

  A Hall effect sensor is provided in which the magnetic structure has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two parts, one of which has an N pole on the front face, and whose other

  has an S pole on the front face.

  A Hall effect sensor is provided in which the magnetic structure has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two parts, one of which has an N pole on the front face, and the other of which has an S pole on the front face, and one of these parts is moved back relative to the face to adjust the field

  magnetic created by the magnetic structure.

  A Hall effect sensor is provided in which the magnetic structure has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two permanent magnets, one of which has a pale N on the front face , and whose other

  has an S pole on the front face.

  A Hall effect sensor is provided in which the magnetic structure has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least one straight permanent magnet and at least one pole piece which is temporarily magnetized by its presence in the magnetic structure, one of which has an N pole on the front face, and of which

  the other has an S pole on the front face.

  A Hall effect sensor is provided in which the magnetic structure has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two permanent magnets and at least one pole piece which is positioned between the permanent magnets and which is temporarily magnetized by its presence in the magnetic structure, one of the permanent magnets having at least one of the magnetic poles on the front face, and the pole piece having the other pole

magnetic on the front.

  A Hall effect sensor is provided in which the magnetic structure has the shape of a cylinder with a magnetic axis and a flat front face adjacent to the chip and

parallel to the collector plane.

  A Hall effect sensor is provided in which the magnetic structure has the shape of a cylinder with a magnetic axis and a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two permanent magnets, of which one has an N pole on the front, and the other

  has an S pole on the front face.

  A Hall effect sensor is provided in which the magnetic structure has the shape of a cylinder with a magnetic axis and a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least one straight permanent magnet and at least one pole piece which is temporarily magnetized by its presence in the magnetic structure, one of which has an N pole on the front face, and the other of which has a pole

S on the front panel.

  A Hall effect sensor is provided in which the magnetic structure is in the form of a cylinder with a magnetic axis and a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two permanent magnets and at minus one pole piece which is positioned between the permanent magnets and which is temporarily magnetized by its presence in the magnetic structure, the permanent magnets having one of the magnetic poles on the front face, and the pole piece having the other pole

magnetic on the front.

  FIG. 7a relates to a construction previously designed with a single pole of the magnet adjacent to the Hall effect element and configured to control the passage of ferromagnetic gears. FIG. 7 is a flow diagram showing the variation in magnetic field as a function of the air gap between the Hall effect element and the gear. The graph is in negative Gauss, so the baseline (between the teeth) is the upper curve of each data line. The amplitude of the data lines increases when the air gap decreases (distance between teeth and sensor). The baseline field is extremely high, i.e. the magnetic force field is 3000 G (actually -3000 G since the pole adjacent to the Hall effect chip is S, so that the flux is negative) for the SmCo magnet used in this case. To work on large air gaps, an extremely small variation in magnetic field must be measured over a large base field. For example, the 80 mil air gap creates a signal of 100 G on a basic field of 3000 G. This is an extremely difficult task. In addition, in some cases, the base field moves, along with the air gap, due to interference between neighboring teeth. When we consider background signal noise, which is always present in real situations, the problem

becomes even more difficult.

  Figure 7b is similar to Figure 7a, except that Figure 7b uses a target with wider teeth

  and a wider space between the teeth.

  FIG. 8 relates to the laminated configuration (in this case, SNS) of the present invention and is a diagram of the flux at power-up of the flux density in Gauss, for various air gaps (distances between teeth and sensor) relative to the rotation of the target (gear). The target is substantially the same as that used in Figure 7b. The zero degrees are in the center of the tooth. The laminated configuration lowers the base field (to approximately -100 G) on the face of the Hall effect element by bringing the two poles of the magnetic field immediately behind the Hall effect element. The close presence of opposite poles is used to short-circuit the flow lines in the open circuit (when the hollow is present and not the tooth). This creates a baseline baseline because the magnetic flux lines are parallel to, and below, the Hall effect element in the chip. Proper design can allow the baseline field to approach zero Gauss as measured by the Hall effect element. When the tooth is present, the magnetic circuit is modified and the flux lines are drawn towards the tooth and

  across and perpendicular to the Hall effect element.

  Then the Hall effect element measures a high value.

  Thus, the tooth creates a diversion or concentration of the flux lines and can also effect or minimize the short-circuiting (or the dispersion field) in the system. The result of this short-circuiting when the tooth is absent, and of diversion or concentration when the tooth is present, is represented by the flow diagram of FIG. 8 which was created by spinning a gear with great pitch in front the sensor with various

  air gaps between the periphery of the teeth and the sensor.

  As shown, the baseline indicating the dip remains constant and of low value (close to zero) as the air gap varies. On the other hand, the flux density, indicating the presence of the tooth, drops (the negative density increases) as the air gap decreases. The flux densities are negative because, at the level of the Hall effect element, the lines of magnetic force enter the S poles, as in the

  previous configuration, and are concentrated by the target.

  Because there is a very significant and easily recognized difference between the tooth-present signal and the tooth-absent signal, at power-up, i.e. when the system is activated for the first time, the sensor of the present invention provides a very reliable indication of this very critical condition, for example, in the distributor of an internal combustion engine for

  minimize air pollution at startup.

  The sign convention used in Hall effect sensors is that a flow from an N pole in front of the

  sensor to an S pole behind the sensor is negative.

  Figure 9 is similar to Figure 8 in that both relate to the laminated configuration of the present invention. FIG. 9 is a flow diagram at power-up of the flux density in Gauss, for various air gaps (distance between teeth and sensor) relative to the rotation of the target (gear). The zero degrees are in the center of the tooth. The laminated configuration lowers the base field (to approximately 75 G) on the face of the Hall effect element by bringing the two poles of the magnetic field towards the rear of the Hall effect element. The close presence of opposite poles is used to short-circuit the flow lines in the open circuit (when the hollow is present and not the tooth). This creates a baseline baseline because the magnetic flux lines are parallel to, and below, the Hall effect element in the chip. An adequate design can allow the basic field to approach zero Gauss measured by the Hall effect element. When the tooth is present, the magnetic circuit is modified and the flux lines are drawn towards the tooth and

  across and perpendicular to the Hall effect element.

  Then the Hall effect element measures a high value.

  Thus, the tooth causes a diversion of the flux lines so as to minimize the short-circuiting (or dispersion field) in the system. The result of this short-circuiting when the tooth is absent, and of diversion when the tooth is present, is represented by the flow diagram of FIG. 9 which was created by rotating a gear at high speed in front of the sensor at various air gaps between the periphery of the teeth and the sensor. As shown, the baseline indicating the dip remains constant and of low value (close to zero) as the air gap varies. On the other hand, the flux density caused by the presence of the tooth increases with the reduction of the air gap. The sign of the flux is positive, because the flux lines at the level of the Hall effect element of this configuration (N-S-N) leave the poles N and are

concentrated by the target.

  Figure 10 shows a flow density diagram across the face of a sandwich magnet (NSN) in which two magnets with N poles on the face are separated by a pole piece which is aligned on the face and has a pole S to the face. The sandwich magnet is 8 mm wide across the face, the pole piece being 1 mm wide and the side magnets being 3.5 mm wide each. In the center of the face and of the pole piece, the flux is -500 G. The value is negative because the point is adjacent to an S pole. When the measurement point moves laterally across the face, the flux is moves towards zero and reaches zero slightly outside the limit of the pole magnet. Then, as the measurement point moves more, the flux increases positively when it moves through the N pole, up to a maximum value of

  1000 G at 1 mm from the limit of the pole piece magnet.

  The measurement tool saturates at, or does not save, a value above 1000 G. It should be understood that this diagram only presents the flow component

  perpendicular to the magnet face.

  Figure 11 shows the effect of the magnet position relative to the rear of the Hall effect element on the strength of the baseline field, for a sandwich magnet with an aligned T-piece. The graph shows the flux density in relation to the position of

  the magnet behind the Hall device for various air gaps.

  Figure 12 shows the effect of moving the pole piece back from the face of the magnet by Z mm on the baseline flux density (hollow present) through the face of a pole piece sandwich magnet in T. It appears that a Z value of 1.25 places the baseline flow

central approximately zero.

  Figure 13 shows a flow diagram through the face of a T-piece sandwich magnet with a piece

fleece moved back 1.5 mm.

  Figure 14 is similar to Figure 13 except that the magnet used to generate the data in Figure 14 is a sandwich magnet in which the center element is an inverted straight magnet (this is not a T and not only

  a pole piece) also moved back 1.5 mm.

  Although the physical principles that allow the present invention to achieve its unexpected beneficial result are not fully understood, the following model provides an effective tool for designing versions of the present invention and for predicting how they will work. This model is based on the model of

"magnetic circuit.

  Figure 15 shows a Hall effect gear tooth detector with a single pole of the type known in the prior art. The cylindrical permanent magnet 13 has flat ends at its N and S poles. A Hall effect sensor 14 is mounted at the end of pole S. The sensor detection plane is perpendicular to the axis NS of the magnet . Because the Hall effect sensor 14 measures the magnetic flux density component perpendicular to the detection plane of the sensor, and because the magnetic flux lines come from infinity and then come together and enter the S pole of the magnet, in parallel to the axis of the magnet, the sensor detects a very large negative magnetic flux (large absolute value) in the normal configuration, and without ferromagnetic material

  in the detection field, as shown in figure 15.

  Thus, the baseline signal generated by the Hall effect sensor has a relatively high absolute value. It is designated as position A on the Hall signal graph in Figure 25 which shows the absolute value of the Hall signal. The configuration shown in FIG. 15 can be considered as a situation in which the ferromagnetic object to be detected is positioned at infinity by

report to the sensor.

  FIG. 16 shows a schematic representation of a gear 11 which is moved to a position relatively distant from the sensor and the gear teeth being positioned on either side of the sensor so

  that the sensor detects the space between the teeth.

  The existence of the ferromagnetic gear in the magnetic flux field causes the flux to collect and concentrate slightly towards the N-S axis of the magnet. The result is that the magnetic flux detected by the sensor increases. This position, designated as position B in Figure 25, is shown as an increased Hall signal. Because the basic signal that would be created by position A, as shown in Figure 15, is relatively strong, the relatively small increase in signal at position B, shown in Figure 16, provides

  a relatively low signal-to-noise ratio.

  When the gear, which is positioned as shown in Figure 16, rotates to bring the tooth to its closest position on the rotational path, as shown in Figure 17, the flux lines come together evenly more significant and the flow density perpendicular to the Hall effect sensor increases even more. This position is shown in the

position D of figure 25.

  Figure 18 shows a gear that is positioned even closer to the sensor. This position of the sensor brings together the intermediate flow lines between position B and position D, shown in Figures 15 and 16, respectively. This is shown in

position C in Figure 25.

  Figure 19 shows the rotation of the gear shown in Figure 18 so that the gear tooth is in its position closest to the sensor. This orientation of the tooth and the magnet pole concentrates the maximum amount of flux directly through the sensor

  and therefore provides the strongest Hall signal.

  Because all the signals generated by positions B, C, D, and E are relatively weak compared to the basic signal which is in position A, the signal-to-noise ratio of the signal generated when the gear rotates in front of the sensor is relatively small. Consequently, the air gap between the gear tooth and the sensor becomes extremely critical for the reliable operation of the

gear tooth detector.

  Figure 20 shows a schematic view of the present invention as it corresponds to the structure of the prior art shown in Figure 15. In Figure 20, the magnetic face on which the Hall effect sensor 14 is mounted is shown as a laminated structure 15. This category of laminated magnets is sometimes called "holding" magnets because they very strongly hold ferromagnetic objects in contact with them. The magnetic structure shown in Figures 20-24 is composed of two standard straight magnets SN 16 and 17 mounted in parallel on a ferromagnetic pole piece 18 having a T-shaped cross section. Because the magnets induce a magnetic field in the room pole, the part of the pole piece adjacent to and between the ends S of the magnet becomes a virtual pole N. Therefore, the magnet acts as if there was an N pole between the two S poles. As shown in Figure 20, the effect of this arrangement of the magnet causes a "short circuit" of the magnetic flux lines so that instead of radiating outward from the face of the magnet to infinity along the magnetic axis, the flux lines adjacent to the axis tend to move in a highly concentrated from the pole N of the pole piece to each pole S. The part of the central pole piece which extends outwards and covers the rear ends of the magnet elements is called the plate. It can be part of the central pole piece or it can be a separate pole piece. It can also be used when the central element is a permanent magnet. The relevant effect of the plate is to increase the front range of the magnetic field in front of the magnetic structure and, therefore, to increase

the capacity of the sensor.

  As it appears in figure 20, the flux lines which are near the axis of the magnet and the Hall effect element, from the pole N of the pole piece to each of the poles S, are highly concentrated very close to the extreme surface of the magnet and move essentially radially outwards from the N pole and the axis of the magnet, and in parallel with the plane of the Hall effect sensor, up to the S poles. Therefore, although there is a very high magnetic flux density very close to the surface of the magnet, the density at the Hall element is very significantly reduced or almost non-existent. Furthermore, because the Hall effect sensor only detects the magnetic flux component that is perpendicular to the plane of the Hall effect element, the Hall effect sensor effectively detects no magnetic flux in the innovative configuration shown in Figure 20. This corresponds to the tooth position F in Figure 25 or a situation where the ferromagnetic object to be detected is at infinity. The Hall signal is approaching zero. FIG. 21 shows the effect of moving the gear 11 to be detected towards a position relatively distant from the sensor. Because the flux density in the present invention also resides near the face of the magnet, the presence of the gear with its tooth overlapping the sensor has almost no effect on the sensor. This position, shown at position G in Figure 25, has only a small

  or almost no effect on the Hall signal.

  Figure 22 shows the effect when the gear shown in Figure 21 turns to bring the tooth close to the sensor. This position is shown at position I in Figure 25. As can be seen, the position close to the gear tooth attracts the magnetic flux, which enters the poles S, axially inward and concentrates the lines of flux near the axis of the magnet and the Hall effect element. Therefore, a substantial amount of flow lines actually pass through the Hall element and have significantly components perpendicular to the plane of the Hall element. Therefore, the signal that is generated at position I is substantially above the position between two teeth of position G in absolute value, that is, in the

  S-N-S configuration, a more negative value.

  Figure 23 shows an arrangement in which the gear, although still in the position between two teeth, is placed even closer to the sensor than in the arrangements shown in Figures 21 and 22. As with the other positions between two teeth shown in FIG. 21, the presence of the gear in its orientation between two teeth is not sufficient to axially concentrate or attract significant quantities of flux lines through the Hall effect element. Therefore, as position H in the figure indicates, there is no significant increase in the

signal with this orientation.

  Figure 24 shows a position in which the rotation of the gear positioned in Figure 23 moves the tooth closest to the sensor. As can be seen in Figure 24, the effect of the ferromagnetism of the gear axially concentrates or attracts a very large amount of flux and flux lines through the Hall effect sensor. Due to the substantial density of the flux across, and perpendicular to, the plane of the sensor, the signal specified in Figure 25 as being generated by position J, Figure 24, is relatively strong (very negative), particularly compared to the signal between two teeth of position H. In addition, it is relatively strong in comparison with the position of baseline at position F, and therefore the signal / noise ratio of the arrangement

is relatively large.

  Figures 26-41 show a series of magnetic structures which represent the principles of the present invention in that they have at least two different poles with a single face. Figure 26 is a perspective view of a magnetic structure which includes four magnetized poles and one face. Figure 27 is a perspective view of a magnetic structure which includes two poles, one face, and a steel plate. Figure 28 is a perspective view of a magnetic structure which includes four poles, one side with a steel plate. Figure 29 is a perspective view of a magnetic structure which includes a pole parallel to the thickness with a steel plate and a central pole. Figure 30 is a perspective view of a magnetic structure which includes a blade parallel to the thickness with a steel cup. Figure 31 is a perspective view of a magnetic structure which includes a pole parallel to

  thickness with a steel cup and a central pole.

  Figure 32 is a perspective view of a magnetic structure which includes three alternating magnets with a

steel tray.

  Figure 33 is a perspective view of a magnetic structure which includes a pole parallel to the thickness with a steel angle. Figure 34 is a perspective view of a magnetic structure which includes a pole parallel to the thickness with a steel channel. The figure is a perspective view of a magnetic structure which includes poles parallel to the thickness with two lateral steel plates. Figure 36 is a perspective view of a magnetic structure which includes two magnetized poles and a face (through). Figure 37 is a perspective view of a magnetic structure which includes three magnetized poles and one face (through). Figure 38 is a perspective view of a magnetic structure which includes two magnetized poles and one face (through), with a steel plate. Figure 39 is a perspective view of a magnetic structure which includes two magnets with a steel tray. Figure 40 is a perspective view of a magnetic structure which includes three magnetized poles and one face (through), with a steel plate. Figure 41 is a series of perspective views of magnetic structures which

  have multiple poles on one side.

  Figure 42 shows a sensor assembly 10 of the present invention in a typical application situation. In this case, the sensor assembly 10 is positioned with its front surface facing the outer periphery of a gear toothed wheel 101 having teeth 102. The gear wheel 101 is coaxial with, and connected to, a wheel mounted on the axle of a vehicle, so that the rotation of the wheel 103 of the vehicle is

  proportional to the rotation of the gear 101.

  The sensor assembly 10 is capable of controlling the passage of the gears in front of the face of the sensor 10 and of producing an electrical signal linked to the speed at which the teeth pass in front of the sensor 10. The electrical signal is processed in a signal processor 105 which in turn passes the signal to the user in a form suitable for use. For example, the sensor can be used to determine the speed of a vehicle, to determine the speed of an engine, and to control the ignition of spark plugs by controlling the position of a cam.

in a distributor.

  Figure 43 is a computer model of the effect of a rectangular ferromagnetic target 11a on the magnetic field around a magnetic structure 15a representing the principles of the present invention. The magnetic structure 15a has two magnets 16a and 17a, and a T-shaped pole piece 18a which has a center piece and a tray. The central part is moved away from the

  front face (towards the target) of the magnetic structure.

  FIG. 44 corresponds to FIG. 43 and shows how the displacement of the target 11a towards the magnetic structure causes the lines of flux between the target and the magnetic structure to concentrate axially inwards. A Hall effect element on the axis and between the target and the magnetic structure would see a higher flux density as the target moves towards the magnetic structure. This model supports the explanation that the targetless magnetic field has a magnetic "neutral zone" along the axis of the magnet and in front of the scattering field, near the front of the magnetic structure. A magnetic field sensor placed in this "neutral zone" would detect very little or no magnetic flux when no target is present, but would detect a flux when the longitudinal flux lines are drawn axially inwards

  by the sensor by the presence of the target.

  As mentioned above, an alternative magnetic structure can be selected which has only

  an N pole and an S pole on the back of the sensor chip.

  Figure 45 shows the flux density across the face of a magnetic structure that has only one N pole

  and an S pole on the back of the sensor chip.

  FIG. 46 shows the gear passing signal produced by the magnetic structure shown in FIG. 45. This is less than the three polar structures,

  but is usable and may be less expensive to produce.

  Although this description has focused on the use

  of a Hall effect element in a magnetic flux detector, the concept of the present invention can be applied to a substitute for the Hall effect element, called a magnetoresistive element. Characteristics of this type

  are specified in Figure 47.

  The use of the magnetoresistive element in the present invention would require that the differences between the two devices be recognized, and in particular that it be recognized that the Hall device is a voltage difference device which detects a flow perpendicular to its plane. , while the magnetoresistive element is a resistance device which detects a flow parallel to the

  plane of the device and perpendicular to the current flow.

  It is obvious that minor modifications can be made in terms of the form and construction of the invention without departing from the material spirit thereof. However, it is not desired to limit

  the invention in the exact form shown and described here.

Claims (31)

  1. Hall effect sensor, adapted to detect a ferromagnetic object (11), characterized in that it comprises: (a) an integrated circuit chip including a planar Hall effect element (14) which is positioned in, parallel to , and defines a sensor plane having a front side and a rear side, and which element is perpendicular to, and centered on, a sensor axis, and (b) a magnetic structure (15) having an N pole and an S pole , the magnetic structure (15) being positioned behind the sensor plane, and positioned so that a pole S and a pole N are adjacent to each other, and the two are adjacent to the element.   2. Hall effect sensor according to claim 1, characterized in that it is adapted to detect the presence   a ferromagnetic object (11) near the sensor.   3. Hall effect sensor according to claim 1, characterized in that it is adapted to detect the distance   between the sensor and a ferromagnetic object (11).   4. Hall effect sensor according to claim 1, characterized in that it is adapted to detect the position   of a ferromagnetic object (11) relative to the sensor.   5. Hall effect sensor according to claim 1, characterized in that it is adapted to detect the speed at which a ferromagnetic object (11) passes in front of the sensor. 6. Hall effect sensor according to claim 1, characterized in that the magnetic structure (15) forms a magnetic detection field in front of the magnet and extends towards the front of the sensor plane, said field imposing a component magnetic flux density in, and perpendicular to, the Hall effect element, the value of the component being linked to the position of the object ferromagnetic in the field.   7. Hall effect sensor according to claim 1, characterized in that the magnetic structure (15) forms a magnetic detection field in front of the magnet and extending towards the front of the sensor plane, said field imposing a component of magnetic flux density in, and perpendicular to, the Hall effect element, the value of the component being linked to the position of the ferromagnetic object in the field, and in that the value of the component has a value of baseline which has an absolute value close to zero Gauss and occurs when the object is   away from the sensor.   8. Hall effect sensor according to claim 1, characterized in that the value close to zero has a value   absolute which is less than or equal to 400 Gauss.   9. Hall effect sensor according to claim 1, characterized in that the distance out of range is greater than or equal to 10 mm.   10. Hall effect sensor according to claim 1, characterized in that the Hall effect element is at a distance of 0.5 to 2.0 mm from the magnetic structure (15). 11. Hall effect sensor according to claim 1, characterized in that the Hall effect element is located   a distance of 1 mm from the magnetic structure (15).   12. Hall effect sensor according to claim 1, characterized in that the magnetic structure (15) has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two parts, including the one has an N pole on the face   front, and the other of which has an S pole on the front face.   13. Hall effect sensor according to claim 1, characterized in that the magnetic structure (15) has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two parts, including the one has an N pole on the front face, and the other has an S pole on the front face, and one of these parts is moved back relative to the face to adjust the magnetic field created by the structure magnetic (15).   14. Hall effect sensor, according to claim 1, characterized in that the magnetic structure (15) has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two permanent magnets, including l 'one has an N pole on the front, and the other has an S pole on the front. 15. Hall effect sensor according to claim 1, characterized in that the magnetic structure (15) has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least one straight permanent magnet and at minus a pole piece (18) which is temporarily magnetized by its presence in the magnetic structure (15), one of which has an N pole on the front face, and the other of which has an S pole on the front face.   16. Hall effect sensor according to claim 1, characterized in that the magnetic structure (15) has a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two permanent magnets and at least a pole piece (18) which is positioned between the permanent magnets and which is temporarily magnetized by its presence in the magnetic structure (15), one of the permanent magnets having at least one of the magnetic poles on the front face, and the piece polar (18) having the other magnetic pole at the front face.   17. Hall effect sensor according to claim 1, characterized in that the magnetic structure (15) has the shape of a cylinder with a magnetic axis and a flat front face adjacent to the chip and parallel to the sensor plane. 18. Hall effect sensor according to claim 1, characterized in that the magnetic structure (15) has the shape of a cylinder with a magnetic axis and a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two permanent magnets, one of which has an N pole on the face   front, and the other of which has an S pole on the front face.   19. Hall effect sensor according to claim 1, characterized in that the magnetic structure (15) has the shape of a cylinder with a magnetic axis and a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least one right permanent magnet and at least one pole piece (18) which is temporarily magnetized by its presence in the magnetic structure (15), one of which has an N pole on the front face, and the another has an S pole on the front. 20. Hall effect sensor according to claim 1, characterized in that the magnetic structure (15) has the shape of a cylinder with a magnetic axis and a flat front face adjacent to the chip and parallel to the sensor plane, said magnetic structure including at least two permanent magnets and at least one pole piece (18) which is positioned between the permanent magnets and which is temporarily magnetized by its presence in the magnetic structure (15), one of the permanent magnets having at least one magnetic poles on the front face, and the pole piece (18) presenting the other magnetic pole at the front face.   21. Hall effect sensor, suitable for detecting a ferromagnetic object (11), characterized in that it comprises: (a) an integrated circuit chip including a planar Hall effect element (14) which is positioned in, parallel to , and defines a sensor plane having a front side and a rear side, and which element is perpendicular to, and centered on, a sensor axis, and (b) a magnetic structure (15) including three magnetized elements, the magnetic structure (15) being positioned behind the sensor plane, and positioned so that the first and second of the magnetized elements each place a first magnetic pole adjacent to the Hall effect element, and the third the magnetized element places the second magnetic pole , who is opposed to said   first magnetic pole, adjacent to the Hall effect element.   22. Hall effect sensor according to claim 21, characterized in that all the magnetized elements are permanent magnets.   23. Hall effect sensor according to claim 21, characterized in that the first and second magnetized elements are permanent magnets and the third   magnetized element is a pole piece (18).   24. Hall effect sensor according to claim 21, characterized in that the first and second magnetized elements are permanent magnets and the third magnetized element is a pole piece (18) interposed   between said two magnetized elements.   25. Hall effect sensor according to claim 21, characterized in that the third magnetized element is a permanent magnet and the first and second elements   magnetized are pole pieces.   26. Hall effect sensor according to claim 21, characterized in that said third magnetized element is interposed between the first and second magnetized elements. 27. Hall effect sensor according to claim 21, characterized in that each element of the magnetic structure (15) has a rear part remote from the Hall effect element, and the magnetic structure (15) includes a   tray that covers all the rear parts.   28. Hall effect sensor according to claim 21, characterized in that each element of the magnetic structure (15) has a rear part remote from the Hall effect element, and the magnetic structure (15) includes a plate which makes part of at least one of the elements and covers all rear parts.   29. Sensor, adapted to detect a ferromagnetic object (11), characterized in that it comprises: (a) an integrated circuit chip including a sensor element which is positioned in, parallel to, and defines a sensor plane having a front side and a rear side, and which element is perpendicular to, and centered on, a sensor axis, and (b) a magnetic structure (15) having an N pole and an S pole, the magnetic structure (15) being positioned behind the sensor plane and positioned so that an S pole and an N pole are adjacent to each other and the   two are adjacent to the sensor element.   30. Sensor, adapted to detect a ferromagnetic object (11), characterized in that it comprises: (a) an integrated circuit chip including a magnetoresistive element which is positioned in, parallel to, and defines a sensor plane having a front side and a rear side, and which element is perpendicular to, and centered on, a sensor axis, and (b) a magnetic structure (15) having an N pole and an S pole, the magnetic structure (15) being positioned behind the collector plane and positioned so that an S pole and an N pole are adjacent to each other, and the   two are adjacent to the magnetoresistive element.   31. Sensor, adapted to detect a ferromagnetic object (11), characterized in that it comprises: (a) an integrated circuit chip including a magnetoresistive element which is positioned in, parallel to, and defines a sensor plane having a front side and a rear side, and which element is perpendicular to, and centered on, a sensor axis, and (b) a magnetic structure (15) including three magnetized elements, the magnetic structure (15) being positioned behind the plane of sensor and positioned so that the first and second of the magnetized elements each place a first magnetic pole adjacent to the magnetoresistive element, and the third magnetized element places the second magnetic pole, which is opposite to said first magnetic pole, adjacent to the element magnetoresistant.